President Barack Obama looks over his notes as he answers questions about the Iran nuclear deal during a news conference in the East Room of the White House, July 15, 2015. AP Part pitchman, part physics teacher, President Barack Obama is taking on the job of selling the Iran-nuclear deal with the gusto of a salesman who won't take no for an answer.

An hour or so into a presidential press conference on the details of the agreement Wednesday, Obama looked like he didn't want it to end.

"Have we exhausted Iran questions here?" he asked, whipping a paper out of his breast pocket to make sure he hadn't missed anything. "I really am enjoying this Iran debate."

The president will have no shortage of opportunities to make his pitch: The deal is generating stormy opposition among Republicans in Congress and even among some Democrats; US ally Israel is adamantly against it; and the case must be made to the American people, who view Iran warily and disapprove of Obama's overall handling of the US relations with that nation.

But after years of up-and-down negotiations on the landmark accord, the president is clearly relieved to have something to sell. And he's clearly steeped in the minutiae of the 100-page agreement.

At his press conference, he argued centrifuges and uranium stockpiles. He sized up political dynamics, both domestic and international.

He challenged his critics to come up with a better alternative — and exuded confidence that they couldn't.

If Iran tries to pull a fast one and set up a covert nuclear program, the president assured, they'll have "some 'splaining to do."

File photos of technicians of Iran's Atomic Energy Organisation in a control room at the Uranium Conversion Facility in Isfahan. Thomson Reuters

Most people won't ever sit through an hour-long defense of the plan, though. So the White House's task is to distill an incredibly complex agreement — this is rocket science, after all, and then some — into talking points that the public can digest without getting lost in the nuclear physics.

That calls for a certain amount of trust, that, yes, the president's got this right. And enough detail to make his assurances ring true, without being overwhelming.

With his detailed defense of the plan, Obama is "reassuring Americans that he knows what he's talking about and they can have faith that he's completely versed in what is a pretty arcane subject," says former White House press secretary Jay Carney.

The White House has been quick to flood social media with a series of colorful slides reinforcing its key messages. One assures people that the deal "achieves what we asked for: preventing Iran from obtaining a nuclear weapon."

Boiling down years of negotiations to its national-security essence, Obama's simplified message is that "every pathway to a nuclear weapon is cut off."

Clearly viewing the Iran deal as a critical part of his legacy, Obama framed the agreement as a defining issue for the fourth quarter of his presidency.

Robust debate is fine, he said, but, "if we don't choose wisely, I believe future generations will judge us harshly for letting this moment slip away."

Opponents of the deal, both at home and abroad, are determined to challenge that narrative.

Israeli Prime Minister Benjamin Netanyahu said Wednesday there were "absurd things" in the agreement, and accused world leaders of falling into "a trap of smiles set by the tyrannical Iranian regime." The New York Times reported in Thursday's edition that when Obama called Netanyahu to discuss the deal this week, the president offered to hold "intensive discussions" to bolster Israel's defenses, citing administration officials. The Israeli prime minister refused to have such conversations at this time, the paper reported.

GOP presidential candidate Chris Christie said Obama was lying to the American people about details of the plan.

Obama said much of the opposition was predictable, and he dismissed domestic complaints as politically motived.

"We live in Washington, and politics do intrude," he said, suggesting he was above all that.

"You know, the facts are the facts, and I'm not concerned about what others say about it," he said.

Concerned or not, he's not about to cede the floor.

"I promise you I will address this again, all right?" he said at the end of his news conference. "I suspect this is not the last that we've heard of this."

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